This disclosure relates to aliphatic polycarbonates and aliphatic-aromatic polycarbonates and their preparation through melt polymerization.
Polycarbonates are ranked among the most important of the world's engineering thermoplastics. Bisphenol A polycarbonate is currently the most widely used polycarbonate and its world wide annual production exceeds one billion pounds. Polycarbonates are used in hundreds of applications such as eyeglass lenses and optical media, where their transparency and tough physical properties are beneficial. Traditionally, polycarbonates have been prepared either by interfacial or melt polymerization methods. The reaction of an aromatic dihydroxy compound such as bisphenol A (BPA) with phosgene in the presence of water, an organic solvent, an acid acceptor and a catalyst is typical of the interfacial method. The reaction of bisphenol A with a source of carbonate units such as diphenyl carbonate in the presence of a catalyst and the absence of solvent is typical of melt polymerization method. Each method is practiced commercially on a large scale. In many cases, desirable properties can be imparted to polycarbonates by reacting together two or more different aromatic dihydroxy components using the melt or interfacial method to form a copolycarbonate. In such cases, it is often desirable to obtain random incorporation of the different dihydroxy compounds into the polymer to achieve certain desirable physical properties, but this may be difficult to achieve by the melt method in cases where the different dihydroxy compounds happen to have differing reactivity. Random incorporation may be similarly difficult to achieve by the interfacial method when the dihydroxy compounds have differing or unacceptably low solubility in the reaction medium. The efficient production of polycarbonates generally involves a number of trade-offs. For example, one can compensate for low reactivity by increasing catalyst concentration, time or temperature but generally each such measure that one takes to make reaction conditions more “aggressive” involves a penalty in terms of increasing the yellowness of the transparent material.
Copolycarbonates including aliphatic diols such as isosorbide are of great interest to the chemical industry because such aliphatic diols can be produced from renewable resources, namely sugars, rather than from petroleum feed stocks as for most presently used diol monomers. Therefore, it would be desirable to have an efficient method to produce high quality, random, low yellowness copolycarbonates from isosorbides. There have been several previous attempts to produce commercial copolycarbonates from isosobides, but each of these attempts has had its difficulties. Presently, such copolycarbonates are not produced commercially.
Thus it is clear that there is a need for an efficient polymerization process to produce isosobide copolycarbonates having good color properties (i.e., low yellowness) and acceptably high molecular weight for commercial application.